Hydrogels are three-dimensional, water-swollen structures composed of mainly hydrophilic homopolymers or copolymers. See, e.g., Lowman, A. M. and Peppas, N. A., Hydrogels, in Encyclopedia of Controlled Drug Delivery, E. Mathiowitz, Ed., John Wiley and Sons, 1999 pp. 397-418. These materials are for the most part insoluble due to the presence of chemical or physical crosslinks. The physical crosslinks can be entanglements, crystallites, or weak associations such as van der Weals forces and hydrogen bonds. The crosslinks provide the network structure and physical integrity. Hydrogels have been disclosed for use in a variety of biomedical applications.
Hydrogels have been used to form articles such as optical lenses. U.S. Pat. No. 4,954,587 discloses copolymers comprising a polymerization product of N,N-dimethylacrylamide, a vinyl monomer, and a cross linking agent which is machinable in a dry state and forms clear hydrogels containing 25 to 75 wt. % water. U.S. Pat. No. 5,292,415 discloses a mammalian body implant, particularly for use as a corneal prosthesis, comprising a hydrogel having azlactone-reactive nucleophilic surfaces, a multifunctional azlactone composition covalently coupled to the nucleophilic surfaces, and a biologically active material coupled to the azlactone group.
In addition to optical uses, published U.S. Patent Application 2002/0006521 discloses use of hydrogels in medical devices such as catheters and artificial kidneys and PCT Application WO 2001/05578 discloses use of hydrogels in thin film wound dressings, subcutaneous drug delivery devices and coatings for catheters. Similarly, published U.S. Patent Application 2001/0027299 discloses medical devices including dilation balloons and guide wires, catheters, stents, stent grafts, grafts, vena cava filters and inflation lumens comprising a hydrogel. Hydrophillic hydrogels have also been proposed for incorporation into flexible dermal patches for treatment of human/animal traumatic burns or skin blisters. See e.g., U.S. Pat. No. 6,348,213. Hydrogel dermal patches have also been proposed for treatment of acne and pimples. See e.g. U.S. Pat. No. 6,455,065.
Hydrogels have also been disclosed as useful materials for nucleus replacement in humans as they can be prepared with mechanical and physiological properties similar to the nucleus itself. U.S. Pat. No. 5,047,055 and U.S. Pat. No. 5,192,326 describe a hydrogel for use in nucleus pulposus replacement that is comprised of 100% semi-crystalline polyvinyl alcohol (PVA). U.S. Pat. No. 5,976,186 discloses a prosthetic nucleus prepared from hydrogels of lightly crosslinked biocompatible homopolymers and copolymers of hydrophilic monomers, HYPAN™ or highly hydrolyzed crystalline PVA, which exhibit an equilibrium, water content (EWC) of from about 30 to about 90%. WO 01/32100 discloses a modified PVA hydrogel for use in intervertebral disc replacement, and more specifically replacement of the nucleus pulposus, which has been stabilized by addition of a second polymer, preferably polyvinyl pyrollidone (PVP) or copolymers of PVP and poly(methyl methacrylate), poly(acrylamide), poly(acrylic acid), poly(acrylonitrile) or polyethylene glycol).
Interpenetrating polymeric network hydrogels comprising temperature-sensitive poly(N-isopropyl acrylamide (PNIPAAm) have been described for use as colorimetric reagents (published U.S. Patent Application 2002/0031841) and in decontaminating, heat reversible polymer particles (U.S. Pat. No. 6,180,326). Increases in temperature have been reported to cause significant pore size decreases in interpenetrating polymeric networks composed of PNIPAAm. See Zhang et al. Journal of biomaterials science 2002 13(5):511-25.